To make power converters and like circuits using transformers smaller and more responsive, there is a trend toward using higher and higher frequency excitation. A major obstacle is the parasitic impedances of the transformers, particularly the leakage inductance, both of the windings and of the leads, interconnections and connected circuitry.
The prior art “matrix transformer”, sometimes called a “flat transformer”, significantly reduced the leakage inductance of the windings, but there is a need for yet more improvement. A matrix transformer may have a single turn primary which passes through a number n of interdependent “elements”. The elements are separate magnetic cores with their associated secondary windings, and often the elements are assembled as “modules” with through holes through which the primary is threaded at final assembly.
A matrix transformer with a single turn primary and n elements will have a ratio of n to one. Because the primary is a single winding passing through all the elements, the currents are constrained to be equal in each element. Usually the secondary windings of the elements are connected in parallel, either directly or at the output of associated rectifier circuits, so the voltages in the elements (and thus the fluxes) are also constrained to be equal.
The patent applications cited above for cellular transformers teach an embodiment of the cellular transformer having cellular metal inserts through which a multiple turn primary winding is wound. With a hole for each turn, each active section of the primary winding has a coaxial location within the hole, for very good coupling and low leakage inductance.
The patent applications cited above for switched-current power converters show diagrammatically matrix transformers wherein the coaxial winding is applied to matrix transformer elements having a single turn primary.